A fuel direct-injection engine, e.g., a gasoline engine, of vehicles is disclosed in U.S. Pat. No. 6,055,955 corresponding to JP-A-2000-501816. The fuel direct-injection engine is configured such that a fuel injector and a spark plug are attached to a cylinder head of the engine.
In an electric control system of this kind of vehicle engine, a fuel injection control and a spark timing control are performed by an ECU based on detection signals of multiple sensors for detecting states of the engine so that the engine is driven in an optimum condition. Recently, it is considered that failure in combustion and ignition is detected by a pressure sensor for detecting pressure inside a cylinder room of the engine. As an example of the pressure sensor, US Patent Publication No. 2006156825 corresponding to JP-A-2006-200974 discloses the structure that a pipe portion is formed integrally in a housing, and a diaphragm for receiving pressure inside a cylinder room directly and a pressure detecting element to which the pressure is transmitted are disposed at an end portion of the pipe portion.
In case that the above-described pressure sensor is attached to the engine, a mounting hole is formed at a cylinder head or a cylinder block, the pressure sensor is inserted into the mounting hole from the outside, and the pressure sensor is fixed to the cylinder head by welding or the like. Because an inlet valve, an outlet valve, an injector and a spark plug or the like are disposed in the cylinder head, it is difficult for the pressure sensor to be further disposed in the cylinder head due to space limitations. That is, the pressure sensor is required to be assembled compactly when the pressure sensor is attached to the engine.
Pressure inside the cylinder room becomes about 10 MPa by combustion pressure, and thereby, the air-tight sealing structure is required between the mounting hole and the pressure sensor. Thus, the mounting structure of the pressure sensor may become complex. Because the pressure sensor is weak against heat generally, the pressure sensor is required to be attached to the engine such that the pressure sensor does not become high temperature and detection reliability is increased. In addition, by welding a small element such as the pressure sensor to a large element such as the cylinder head, a large welding apparatus may be required, the workability of assembling may be decreased, and the manufacturing cost may be increased.